International audienceThe mechanisms regulating megakaryopoiesis and platelet production (thrombopoiesis) are still incompletely understood. Identification of a progenitor with enhanced thrombopoietic capacity would be useful to decipher these mechanisms and to improve our capacity to produce platelets in vitro. Differentiation of peripheral blood CD34(+) cells in the presence of bone marrow-human mesenchymal stromal cells (MSC) enhanced the production of proplatelet-bearing megakaryocytes (MK) and platelet-like elements. This was accompanied by enrichment in a MK precursor population exhibiting an intermediate level of CD41 positivity while maintaining its expression of CD34. Following sorting and sub-culture with MSC, this CD34(+)CD41(low) population was able to efficiently generate proplatelet-bearing MK and platelet-like particles. Similarly, SR1, an antagonist of the aryl hydrocarbon receptor (AhR) transcription factor known to maintain CD34 expression of progenitor cells, led to an enriched CD34(+)CD41(low) fraction and to an increased capacity to generate proplatelet-producing MK and platelet-like elements ultrastructurally and functionally similar to circulating platelets. The effect of MSC, like that of SR1, appeared to be mediated by an AhR-dependent mechanism since both culture conditions resulted in repression of its downstream effector CYP1B1. This newly described isolation of a precursor exhibiting strong MK potential could be exploited to study normal and abnormal thrombopoiesis and for in vitro platelet productio

Alpha4A-tubulin is the predominant α-tubulin isotype in platelets. Mutations in α4A-tubulin cause abnormal platelet biogenesis and marginal band formation in mice and in a patient, establishing an essential role of this tubulin isotype.